Contact assembly for an electronic musical instrument

ABSTRACT

An improved contact assembly for an electronic musical instrument in which the distance between a fixed element and the fixed end of a movable element, the distance between an actuator and the fixed end of the movable element, the stroke length of the actuator between the position of first contact of the movable element with the fixed element and the most depressed position of the actuator, the length of a horizontal portion of the movable element, the angle of an inclined portion of the movable element with respect to a horizontal base line, and the distance between the fixed element and the horizontal base line are such that the ratio of the amount of slide of the movable contact element on the fixed contact element in a push direction to that in a pull direction during operation of the contact assembly is from about 1:1 to about 1:2.

United States Patent [72] Inventor Shin-ichi Murakami I-1arnamatsu-shi, Japan 21 Appl. No. 3,905

[22] Filed Jan. 19, 1970 [45] Patented Nov. 9, 1971 Nippon Gaklti Seizo Kabushiki Kaisha Hamamatsu-shl, Shlzuaka-ken, Japan [73] Assignee [32] Priority Jan. 21, 1969 [33] Japan [54] CONTACT ASSEMBLY FOR AN ELECTRONIC 5/1967 Schwartz et al 200/166 J X 3,480,744 11/1969 Yamada Primary ExaminerI-I. 0. Jones ABSTRACT: An improved contact assembly for an electronic musical instrument in which the distance between'a fixed element and the fixed end of a movable element, the distance between an actuator and the fixed end of the movable element, the stroke length of the actuator between the position of first contact of the movable element with the fixed element and the most depressed position of the actuator, the length of a horizontal portion of the movable element, the angle of an inclined portion of the movable element with respect to a horizontal base line, and the distance between the fixed element and the horizontal base line are such that the ratio of the amount of slide of the movable contact element on the fixed contact element in a push direction to that in a pull direction during operation of the contact assembly is from about 1:1 to about 1:2.

PATENTEDuuv 9 l97| sum 2 or 2 FIG. 4

ATTORNEYS CONTACT ASSEMBLY FOR AN ELECTRONIC MUSICAL INSTRUMENT The present invention relates generally to a contact assembly for an electronic musical instrument including a fixed contact element of electrically conductive rubber or like elastic material and a movable contact element of electrically conductive metallic material, and more particularly to a contact assembly so constructed as to minimize the noise which may be generated when the both elements contact with each other.

l-Ieretofore, metallic contact elements have been commonly used in a contact assembly of a keyboard switch for an electronic musical instrument; But tones produced by the electronic musical instrument employing such metallic contact elements are not pleasing to the ear and musically undesirable because accompanying clicking sound due to the abrupt switching of the elements or due to the fact that they make no gradual contact with each other. Recently, however, in order to solve this problem, contact elements made of electrically conductive rubber or like elastic material (which will be hereinafter referred to as elastic contact element) have become used as fixed contact elements in a contact assembly. The elastic contact element makes gradual contact with a movable metallic contact element during the operation of a key and effectively prevents the occurring of the clicking sound as may be generated by the abrupt switching of metallic contact elements. The fixed elastic contact element, however, has a certain disadvantage as described below.

In a contact assembly using such an elastic contact element, the clicking sound does not occur but there is another problem of noise. According to my research, this noise is mainly due to the sliding movement of the movable metallic element on the fixed elastic contact element of the contact assembly. That is, l have found that noise is likely to emanate from the rubbed elastic contact element because it has a physical property of elasticity and because its coefficient of friction is larger than that of the metallic contact element. Further, I have found that such noise can be reduced to a minimum by making the movable element slide on the fixed elastic element in reciprocal manner (i.e. the former slides on the latter in one direction and then turns back and slides in the opposite direction), with minimum sliding distance. That is, in the case of the contact assembly using a fixed elastic contact element the sliding distance must be reduced to a minimum, in contrast with the case of the contact assembly using metallic movable and fixed contact elements in which the movable element is so designed that it slides on the fixed element with a rather long sliding distance in order to obtain self cleaning action at their contact areas.

It is an object of the present invention to provide a contact assembly for an electronic musical instrument in which the noise due to the sliding movement of the movable metallic contact element on the fixed elastic contact element is avoided.

The invention will be explained with reference to the drawings, in which:

FIG. 1 is a side view showing a keyboard switch for an electronic musical instrument;

FIG. 2 is a diagrammatic side view showing a contact assembly of the keyboard switch;

FIG. 3 is a diagram showing relationship between stroke of actuator and contacting position of the movable and fixed contact elements on the movable element; and

FIG. 4 is a diagram showing forms of sliding movement of the movable contact element.

Referring to the drawings, the keyboard switch shown in FIG. 1 includes a fixed elastic contact element 1 made of electrically conductive rubber or other elastic material and a movable contact element 2 arranged at substantially right angles to said fixed contact element and made of gold-plated metallic wire. The fixed contact element 2 is arranged in transverse direction in a frame 3 of the keyboard switch, while the movable contact element 2 is arranged in longitudinal direction therein. The movable contact element 2 is fixed at its one end 4 on the frame 3 and is movable at its other end.

The movable element 2 includes a horizontal portion 5 extending along a horizontal base line thereof and an inclined portion 6 extending from the end of the horizontal portion 5 at an angle to said horizontal base line. An actuator 7 slidably mounted in the vertical direction in the frame 3 engages with the inclined portion 6 of the movable contact element 2. When the actuator 7 is depressed by a key 8 of the electronic musical instrument, it acts to move the movable contact element downward into contact with the fixed contact element 1 (first stage of the stroke of the actuator) and then deform said movable contact element while producing sliding movement of the movable contact element on the fixed contact element (second stage of the stroke of the actuator).

Now the sliding movement of the movable element on the fixed element will be explained more in detail with reference to FIG. 2 which is a diagrammatic view showing the relationship between the fixed elastic contact element 1 and the movable metallic contact element 2. In FIG. 2, the movable contact element 2 is shown in its free condition with no actuator assembled therewith, where the inclined portion 6 is arranged at an angle 0 with respect to a horizontal base line 9. When the element 2 is assembled with the actuator 7, it is lowered to the position shown by a broken line 2. As the key 8 is depressed, the element 2 is lowered to the position shown by a dot-and-dash line 2" the first stage of the stroke of the actuator 7) to make contact between the movable and fixed contact elements and then it is deformed to the position shown by a double dot-and-dash line 2" (the second stage of said stroke) while maintaining the contact between the movable and fixed contact elements. During the second stage of the stroke, the movable contact element 2 makes sliding movement on the surface of the fixed elastic element 1. There are two forms of the sliding movement, namely, a unidirectional sliding movement and a reciprocal sliding movement, depending on the shape of the movable contact element and the relative position of the movable and fixed contact elements. In the unidirectional sliding movement, the movable contact element slides in push or pull direction on the fixed elastic contact element, and in the reciprocal sliding movement the movable contact element slides in the push direction and then turns back and slides in the pull direction.

Throughout this specification, the push direction means the direction in which the contacting position of the movable and fixed contact elements on the movable element moves towards the fixed end of the movable element as the key is depressed, while the pull direction means that in which said contacting position moves towards the free end portion of the movable element.

FIG. 3 shows the relationship between the stroke of the actuator and the contacting position of the movable and fixed contact elements on the movable element in the push and pull directions. In FIG. 3, the curves C and C illustrate the unidirectional sliding movement in the pull direction. The curves C and C illustrate the reciprocal sliding movement, wherein the curve C;, illustrates the case where the ratio of the sliding distance X in the push direction to the sliding distance X in the pull direction is 1:2 and the curve C illustrates the case where the ratio of the sliding distance Y in the push direction to the sliding distance Y in the pull direction is 1:1. The curves C and C shown the unidirectional sliding movement in the push direction.

Upon extensive research on the sliding movement of the contact assembly, I have found that the form of the sliding movement depends on the distance A between the fixed contact element and the fixed end 4 of the movable contact element, the distance B between the actuator 7 and the fixed end 4 of the movable contact element, the stroke S of the actuator until the actuator reaches the most depressed position after the movable contact element has come into contact with the fixed contact element (namely, the above-mentioned second stage of the stroke of actuator), the length L of the horizontal portion 5 of the movable contact element, the angle 0 of the inclined portion 6 with respect to the horizontal base line 9 and the distance 1 between the fixed contact element and the horizontal base line 9. Further I have found that the noise due to the sliding movement of the movable contact element on the fixed contact elements can be reduced to a minimum by so setting the above factors that the movable contact element makes a reciprocal sliding movement on the fixed elastic contact element and that the ratio of the sliding distance in the push direction to that in the pull direction is from about 1:1 to about 1:2.

In the above factors, the distance A, the distance B and the stroke S are substantially constant, depending on the size of the contact assembly. Consequently, the best result can be obtained by the setting of the length L, the angle and the length 1.

FIG. 4 illustrates the form of the sliding movement, wherein it is assumed that A=45 mm., B=30 mm. and S=l.25 mm. In

FIG. 4, the ordinate indicates the length L and the abscissa indicates the angle 0. The curves D,, D D D,, and D and the curves E,, E E E, and E illustrate the boundary lines between the unidirectional sliding movement and the reciprocal sliding movement, in the case where l=l mm., 1=2 mm., 1=3 mm., 1=4 mm., and I=5 mm., respectively. For example, assuming that I=l mm., the movable element makes unidirectional movement in the pull direction in the area above the curve D,, unidirectional movement in the push direction in the area below the curve E, and reciprocal movement in the push and pull directions in the area between the curves D, and 12,. Thus, the area indicated by U, above the group of the curves D,--D is a unidirectional sliding range wherein the movable contact element makes sliding movement in the pull direction, independently of the value of the distance I, while the area indicated by U below the group of the curves E,D is another unidirectional sliding range wherein the movable contact element makes sliding movement in the push direction, independently of the valve of the distance 1. The area indicated by R between the groups of the curves D,-D and E,-E, is a reciprocal sliding range where the movable contact element makes sliding movement in the push direction and then in the pull direction.

The area T, enclosed by the upper group of the curves D,D and the area T, enclosed by the lower group of the curves E,-E are ranges where the movable contact element makes either unidirectional sliding movement or reciprocal sliding movement, depending on the value of the distance I provided that the 1 changes from 1 mm. to 5 mm.

It will be apparent from FIG. 4 that the reciprocal sliding movement can be obtained by selecting the values of L and 0 which fall within the area R, independently of the value of I, provided that A=45 mm., B=30 mm., S=l .25 mm., and l=l5 mm. It has been found that the best result can be obtained in the middle portion of this area R, where the ratio of the sliding distance in the push direction to that in the pull direction is from about 1:1 to about 1:2. According to my experiment, it has been found that such middle portion can be expressed by the following formula:

L(mm.)=%(mm./degree)6(degree):2.5(mm.) where l0 0 30. For example, the best result was obtained when A=45 mm., B=30 mm., S=l.25 mm., L=5 mm., 0=20 and i=2 mm., and the noise due to the sliding movement of the movable contact element on the fixed contact element was reduced to minimum.

Although the forms of the sliding movement were indicated by the values of L, 0 and lwith reference to the particular contact assembly wherein A=45 mm., B=30 mm. and S=l.25 mm., the diagram shown in FIG. 4 is equally applied in general to other contact assemblies by indicating the forms of the sliding movement by the values of L/A, 0 and HA, if B/A =2/3 and S/A=l.25/45 It will be understood that the present invention is based on the extensive research on the sliding movement of the movable contact element on the fixed contact element and provides a contact assembly for an electronic musical instrument in which the noise due to the sliding movement is reduced to minimum.

1 claim:

1. In a contact assembly for an electronic musical instrument including a fixed contact element made of electrically conductive elastic material, a movable contact element made of electrically conductive metallic material arranged at substantially right angle to said fixed contact element and fixed at its one end and means for actuating said movable contact element, said movable contact element having a horizontal portion extending along a horizontal base line thereof and an inclined portion extending from end of said horizontal portion at an angle to said horizontal base line; the improvement wherein a distance A between the fixed contact element and the fixed end of the movable contact element, a distance B between said actuating means and the fixed end of the movable contact element, a length of stroke of said actuating means between a position in which said actuating means moves said movable contact element into initial contact with said fixed contact element and the most depressed position of said actuating means, a length L of said horizontal portion of the movable contact element, an angle 0 of said inclined portion of the movable contact element with respect to the horizontal base line and a distance I between the fixed contact element and the horizontal base line are such that the ratio of the amount of slide of the movable contact element on the fixed contact element in a first direction to that in a second direction during operation of the contact assembly is from about 1:1 to about 1:2.

2. An improvement according to claim 1, in which the length L of the horizontal portion of the movable contact element and the angle 0 of the inclined portion of the movable contact element with respect to the horizontal base line are set to satisfy the following formula: L(mm.)=%(mm./degree)0 (degree)i:2.5(mm.)

where 10 6 30. 

1. In a contact assembly for an electronic musical instrument including a fixed contact element made of electrically conductive elastic material, a movable contact element made of electrically conductive metallic material arranged at substantially right angle to said fixed contact element and fixed at its one end and means for actuating said movable contact element, said movable contact element having a horizontal portion extending along a horizontal base line thereof and an inclined portion extending from end of said horizontal portion at an angle to said horizontal base line; the improvement wherein a distance A between the fixed contact element and the fixed end of the movable contact element, a distance B between said actuating means and the fixed end of the movable contact element, a length of stroke of said actuating means between a position in which said actuating means moves said movable contact element into initial contact with said fixed contact element and the most depressed position of said actuating means, a length L of said horizontal portion of the movable contact element, an angle theta of said inclined portion of the movable contact element with respect to the hOrizontal base line and a distance l between the fixed contact element and the horizontal base line are such that the ratio of the amount of slide of the movable contact element on the fixed contact element in a first direction to that in a second direction during operation of the contact assembly is from about 1:1 to about 1:2.
 2. An improvement according to claim 1, in which the length L of the horizontal portion of the movable contact element and the angle theta of the inclined portion of the movable contact element with respect to the horizontal base line are set to satisfy the following formula: L(mm.) 1/4 (mm./degree) theta (degree) + or - 2.5(mm.) where 10* < theta <30* . 